Solar cells, and specifically photovoltaic (PV) cells, are widely used to convert solar radiation into electrical energy. Solar cells can be fabricated on a semiconductor wafer, using semiconductor processing technology. For example, a solar cell can be fabricated by forming p-doped and n-doped regions on a silicon substrate. Solar radiation impinging on the solar cell creates electrons and holes that migrate to the p-doped and n-doped regions, thereby creating voltage differences between the doped regions.
Certain crystalline-silicon PV cells can be based on back-contact (or rear-contact) design, which seeks to minimize front-side metallization and to maximize working cell area. In such back-contact solar cells, the doped regions are coupled to conductive leads or pads on the backside of the solar cell to allow external electrical circuits to be coupled and powered by the solar cell.
Several solar cells can be connected together to form a solar cell array. In a solar cell array, a conductive area (e.g., a positive solder pad) coupled to p-doped region of one solar cell can be connected to a conductive area (e.g., a negative solder pad) coupled to an n-doped region of an adjacent solar cell. The p-doped region of one solar cell is thus connected to an n-doped area of an adjacent solar cell. Chaining of solar cells can be repeated to connect several solar cells in series, thereby to increase the output voltage of the solar cell arrays. One method of connecting back-contact solar cells is described in U.S. Pat. No. 7,390,961 to Aschenbrenner, et al. (the '691 patent). The '691 patent describes a solar cell module having solar cells interconnected as a solar cell array. An interconnect assembly electrically connects the backsides of two adjacent solar cells. The interconnect assembly has an interconnect that electrically connects a contact point on a backside of a solar cell to a contact point on a backside of another solar cell. The interconnect assembly can further include an interconnect shield placed between the solar cells and the interconnect.
Considering individual solar cells, defects in such solar cells are typically localized, such that solar cells can be diced and the defective portion of the solar cell discarded. FIG. 1 is a diagram illustrating a prior art method by which solar cells can be diced into equal thirds, and a defective portion discarded. Specifically a solar cell 100, having a series of positive solder pads 102 disposed adjacent a first edge, and a series of negative electrical polarity contacts in the form of solder pads 104 disposed adjacent an opposite edge, includes a defective location 106. By dicing the solar cell 100 into thirds (e.g., sections 108, 110 and 112), up to two thirds of the solar cell can be “re-harvested” or recovered. This is possible, in the shown example, because each of the sections 108 and 112, which excludes the defective location 106, has respective positive and negative solder pads disposed adjacent opposed ends thereof. Accordingly, these sections 108 and 112 can be connected in series.
While the dicing method shown in FIG. 1 facilitates re-harvesting of a certain portion of a solar cell, the reliability of a solar array in which the cell sections 108 and 112 are used can be negatively impacted by the loss of redundancy in the solder pad interconnections. For example, if a solder joint between connected positive and negative solder pads of sections 108 and 112 were to fail as an open circuit, the performance of the solar array drops significantly because a bypass diode may need to be activated, and the string in which the sections 108 and 112 are deployed will no longer contribute to the total power production of the relevant solar array. Additionally, if a solder joint fails as a high-resistance connection, there exists a potential for a resistive heating or arcing scenario.